The present invention is related to a compression punch for a rotary press, with a shaft, a punch head disposed at one shaft end and a compression zone disposed at the other shaft end, wherein the punch head features an upper mirror surface, an outer cylinder surface and a curved transition zone between the mirror surface and the cylinder surface. Rotary presses for the production of tablets and similar pressed articles feature lower and upper punches, which co-operate with die bores in a die plate in order to process powder filled in to pressed articles. The moulds with which the punches co-operate are designated as dies, which are fixed as separate sleeve-like inserts in bores of the die plate. In the rotary presses, such compressions punches are used which have a shaft at whose one end is disposed a punch head, and at the other end a compression zone which co-operates with the die bores in order to compress the powder. On its upper side, the punch head has a usually planar mirror surface which co-operates with compression rollers of the rotary press. The diameter of the mirror surface determines the pressure hold time of the compression punches, i.e. at given speed the time duration in which the compression punches interact with the powder to be compressed. The punch heads have a cylinder surface in addition and a transition zone that is disposed between the cylinder surface and the mirror surface and usually rounded. Known punch heads are designed with geometrically defined radii and straight lines. At their lower side, the punch heads verge into the shaft in an e.g. conical zone. The geometric shape and dimensions of punch heads for rotary presses are standardised by DIN ISO 18084:2006-09, which is hereby incorporated by reference in its entirety. However, with known punch heads there is a significant noise emission and a wear on punches and compression rollers in the course of the interaction between the compression rollers and the punch heads. The punch head in particular experiences increased wear at the transition to the mirror surface. Moreover, in the state of the art, just with smaller punch formats the pressure hold times are relatively small, so that materials that are compressible only with difficulty may pose a problem. Finally, increased vibrations of the machine stand take place under certain conditions of operation in the state of the art, leading also to increased emission of noise. In DE 10 2007 043 582 B3, the entire contents of which are hereby incorporated by reference, it is proposed to provide punch heads with chamfers at opposing sides, so that the same may be positioned at smaller distances from each other. This improves the interaction with the compression rollers.
Starting from the explained state of the art, the present invention is based on the objective to provide a compression punch of the kind mentioned in the beginning, wherein the noise emission in the operation is reduced and the wear of the punch heads and the compression rollers is reduced further.